Telephone system



Aug. 13, 1940. B. A. HENsLER 2,211,115

kTELEPHONE SYSTEM Filed argh ll, 1957 ll Sheets-Sheet l 0.92 [Gl D GL ,klll y @up W 1 Aug. 13, 1940- B. A. HENsLER l 2,211,116

TELEPHONE SYSTEM Filed llarch ll, 1937 11 Sheets-Sheet 2 fik/W3 y 272 veyzr:

TELEPHONE SYSTEM Filed March l1, 193'7 l1 Sheets-Sheet 3 Aug. 13, 1940. B. A. HENSLER 2,211,116

TELEPHONE SYSTEM Filed llarch ll, 1937 1l Sheets-Sheet 4 f1@ dr, 7% @MQW Aug. 13, 1940. B. A. HENSLER 2,211,116

TELEPHONE SYSTEM l Filed March l1, 1937 l1 Sheets-Sheet 5 Aug 13, 1940- B. A. HENsLER 2,211,116

TELEPHONE SYSTEM F'l'ed llarch l1, 1937 l1 Sheets-Sheet 6 f@ C@ Wwf? Aug, 13, 1940. B. A. HENSLER 2,211,116

TELEPHONE SYSTEM Filed la rsh ll, 1937 ll Sheets-Sheet 7 Aug. 13, 1940 B. A. HENsLER 2,211,116

TELEPHONE SYSTEM Filed March 1l, 1937 l1 Sheets-Sheet B ICI-6.8.

- Ii C CMQl W dum@ CWI/3 r3@ MQJrM' can@ Aug. 13, 1940. B. A.HENsLER TELEPHONE SYSTEM l1 Sheets-Sheet 9 Filed March ll, 1937 .i Q. u a v, w T/41.40 .W nrw TAW 1 5 ,mJ W 8 3 @M 4 Z :Twllmm X 1f/1# @E .0 r w f .1 s @M B ll/ Tw e mi@ m, m IH M m AU8 13', l940- B. A. HENsLER 2,211,116

TELEPHONE SYSTEM Filed March 11, 1957 11' sheets-sheet 1o Aug. 13, 1940. B. A. HENsLER i 2,211,116

TELEPHONE SYSTEM Filed March 1l, 1937 I V 11 Sheets-Sheet l1 Patented Aug. 13, 1940 TELEPHNE SYSTEM Bernard Anthony Hensler, London, England, assignor to Siemens Brothers t Company Limited, Landon, England Application March l1, 1937, Serial No. 130,388 in Great Britain March i6, 1936 s6 claims. (el. ris-2i) The present invention relates to telephone systems and more particularly to systems in which connections are set up between exchanges over automatic selecting switches. The invention is especially applicable to systems in which trunk calls are set up by an operator.

Although the invention is primarily concerned with trunk switching, several of its features are applicable to short inter-exchange switching.

The trunk system contemplated in this invention is one in which there arey a number of trunk exchanges and in which the completion of a trunk connection may involve the serial connection of inter-exchange trunks. To one or 15 more of these inter-exchange trunks which are direct trunks between two exchanges, alternative routes involving a further exchange or exchanges are provided. A trunk connection is set up in stages and at each exchange at which automatic switching apparatus is situated, digits characteristic of the next exchange through which the call would normally pass are received. To enable a iiexible and economical layout of the trunk selecting switches, translating arrangements are provided and this permits the digits assigned to an exchange to bear some resemblancs, if desired, to the exchange name. For this to be carried out register sending and translating arrangements are provided in the trunk exchanges. The provision of such arrangements besides dealing with calls originating at the'several exchanges enables an indirect or alternative route betwen normally adjacent exchanges to be selected automatically at any stage of a connection should no direct inter-exchange trunk be free and enables additional impulses to be generated automatically and transmitted for setting automatic selecting switches in exchanges in the indirect route. It is a feature of the invention that group control arrangements are associated with the several trunk groups which so control the register sender that a transmission of digits for selecting an alternative route involving a further exchange takes place without loss of time due to search having previously to be made in a group of direct trunks to determine that all such trunks are busy. The group control arrangements are continuously operative so that when a register sender has received the digits denoting the exchange to which the connection is to be extended, the translating arrangements test for an indication of the condition of the trunk routes available and transmit the route selecting digits for the' free route, preference being given to the direct trunk route, m-

mediately. The translating arrangements may be such that simultaneous translations for each route are made, the translation to be made effective depending on the result of the test by the translating arrangements. The arrangements also provide for routing the call to a storage equipment in case of congestion in trunk routes and may also provide for routing a call to a manual board position should difficulty be experienced in selecting a route automatically. The whole or a part of a connection may be set up by an operator at the trunk exchange at the centre at which the call originates.

in a trunk system, especiaily in one that is in a state of development, some of the exchanges may be manually operated. in such a case the arrangements may be employed at those exchanges possessing automatic switching apparatus, the seizure of a trunk resulting in the signalling of an operator at the manual exchange.

The operator so signalled would then complete the setting up of the connection in the usual manner.

As regards control of the trunk selectors the use of group control in conjunction with the translating arrangements obviates search over busy outlets to direct trunks before making a search in a group of alternative route trunks, the selecting switch being directed immediately to a group in which it is known that a free outlet will be found. Should the only free outlets in this group be taken before a searching selecting switch reaches them, arrangements fc-r dealing otherwise with the call become operative.

rilhus the call may be routed to a manual board at the point at which congestion is encountered but if this point is at an exchange in an indirect route it may be more convenient to release the connection back to the point of diversion from the direct route and call in the aid of an operator at the trunk exchange at that point. At an exchange at which an operator sets up the Whole or a part of a connection, hereinafter referred to as an originating exchange, it may be more convenient to release the indirect route set up and direct the switches again to outlets of a direct route, arrangements being made for storing the call. Congestion at first and incoming vtrunk selectors searching for an outlet 'to a second selector may be dealt with by causing the selector to make a further search in the same group after the lapse of a time interval, a second failure to iind a free outlet causing the connection to be routed to a manual board. Group control arrangements enable these facilities to be carried out.

The trunks used in an indirect route may be the same as those normally used in a direct route between the pair of exchanges in question and as such may appear only once in the selecting switch multiple. As regards the connection of trunks in the banks of the trunk selecting switches, these may be connected in any convenient manner and the position in the selector banks of trunks of an indirect route need bear no particular relation to that of the direct trunks to which they offer an alternative and may even be taken from diierent groups of selecting switches.

The register sending and translating arrangements, which also include the apparatus responsive to received digits differ somewhat according to whether they are required to deal with digits originating at the exchange at Which they are situated or with digits incoming over a trunk from a preceding exchange. In general the digits at an originating exchange may be transmitted from a key sender direct to registers while digits incoming from another exchange may be in the form of impulses, either makes end brakes of a circuit over one or both of the line wires, or the transmission thereover of pulses of alternating current of suitable frequency. While the general method of translation and digit sending may be similar in the two types of register sending apparatus, diierent methods of control may be required, as for instance in the one case no reversion of the call to a preceding exchange will be required.

In carrying out the invention it may be arranged that all trunk lines are connected in the banks of second trunk selectors access to which is had over rst or incoming trunk selectors. In addition to outlets to second trunk selectors the iirst or incoming trunk selectors may have outlets to local selectors for the completion of calls locally. To reach the next trunk exchange through which a call must be set up there may be a group of direct trunks and a group of indirect trunks involving one or more additional exchanges. This latter group besides serving as indirect trunks to a more distant exchange may serve as direct trunks to a nearer exchange and would normally be considered as such. Accordingly they may be taken from the same or different groups of second trunk selectors. In the second trunk selector each group of trunks has a call storing position to which the switch proceeds if at the time of search it is unable to nd a free trunk. The arrangements provide that if the selector is searching a trunk group as an indirect route the call is not stored but the switch is stopped on some other contact and a signal is reverted, for example, by the application of a suitable potential to one of the marking wires, to the register sender to bring about release of the connection so far set up in the exchange in question and cause an attempt to be made to set up a direct trunk connection. However, since all the direct trunks are engaged, the second trunk selector advances to the storing position and the call is stored. In the case of an exchange other than an originating exchange it may not be convenient'l to store the call and provision may be made in this case to route the call to a manual operator. If it is known at the time the digits characterising the next exchange along the route are received that no :free trunks of either kind are available, the call may berouted-immediately to the manual operator. 'I'he first trunk selector is provided with an overflow outlet to which it proceeds if all the outlets in the desired direction are busy and from which a signal is sent to the register sender to bring about a further search after a time interval. On reaching the overflow outlet for the second time the circuit arrangements may provide for the release of the sender and the transmission to the operator of an appropriate signal.

The first trunk selectors are connected directly to a connecting circuit, and the common apparatus for the control of a number of selectors may be situated in a common position circuit. The position circuit also includes a key strip and relays for changing over the Wires to the register sender from the key strip to the selector circuit.

The second trunk selectors also may have only a small amount of apparatus individual to them, circuits conmion to a number of selectors and associable with any one of them containing the apparatus necessary for the control of the setting of the selectors. Both the rst and second trunk selectors are adapted to be set by the marking method.

Routing relays operated under the control of group control arrangement-s provide for the application of marking connections for the control of the selectors concerned to cause them to search directly among outlets in which it is known that a free outlet is available at that time. The marking connections for the direct and indirect routes may include different wipers of a translating switch in the register sender. At an intermediate exchange the register sender is adapted to receive a signal that congestion has been encountered and depending on which the register sender is at an exchange in a direct or indirect route to route the call accordingly.

A specific embodiment of the invention as applied to a system in which all the trunk exchanges contain automatic switching apparatus will now be described, the digit registering and sending arrangements being illustrated in the accompanying drawings. Of these Figs. 1 8 show register sending arrangements for use at an originating exchange, Fig. 9 shows so much of an incoming selector at an intermediate exchange as is necessary for the understanding of the invention and Figs. l0 and 11 show register sending arrangements at an incoming exchange. For the sake of example it has been assumed that all the digits necessary for the setting up of the connection are transmitted from the exchange at the centre from which the call is made. With regard to the arrangements at an originating exchange, it should' be explained that calls from a subscriber in the area in which the originating exchange is situated are distributed by means of automatic distributor switches to operators positions. An operators position has a cordless connecting circuit the incoming side of which is connected to the multipled contacts in the banks of the distributing switches and the outgoing side of which is connected to a rst trunk selector. The connecting circuit includes relays for splitting the circuit and con-v equipment, a set of digit keys by means of which the operator may key up any number for transmission to the register sender, and a dial for transmitting impulses over trunks to other exchanges. It also includeskeyslor the control of relays inthe individual connecting circuit and a lamp which indicates to the operator the condition of anygroup of trunks, the code designation of which she has transmitted by her keys to the register sender. The rst trunk elector is a outlet single motion motor-driven switch which givesaccess to second trunk selectors and to link circuits leading to local automatic selecting switches for the. completion of calls within the local area.

The rstv trunk selector is set by markings applied by code relays which are operatedY singly or in combination by code signals transmitted from the register sender. For the transmission ofv digits to the register sender the digit key strip is connected to the signalling wires denoted by W, X, Y, Z in Fig. 1, and when the transmission of digits from the sender is to commence the digit key strip is disconnected from the signalling wires and thelatter are connected to one or other side of the connecting circuit, depending on the keys thrown by the Operator. For the purpose of the present description it will be taken that the signalling wires are connected to that side of the connecting circuit connected to the first trunk selector. To this connection are connected the four code marking relays for receiving the code marking and for marking the rst trunk selector accordingly. At the end of the bank of the first trunk selector are situated overflow contacts to which the wipers rotate and on which thevare brought to rest if search in the marked group has been unsuccessful. In this position a signal in the form of battery potential is transmitted over the wire Y to the register sender to bring about results which will appear in the detailed description to follow. The complete cir-- cuit arrangements oi the connecting and position circuits of the rst trunk selector are assumed to be as; described and shown in British specification No. 8,378/36.

Access to trunk lines is had over a second trunk selector. This is also a motor-driven single motion 1GO-outlet switch with a common control circuit. Like the rst trunk selector it is set by a marking applied by code relays situated in the common control circuit. In the banks of this selector are connected trunks to adjacent exchanges i. e., exchanges next to be encountered in the setting up of a trunk connection toa more distant exchange. The direct trunks to one exchange may serve as trunks in an indirect or alternative route to another exchange. Thus, if the selector is situated at exchange A and there are direct trunks to exchanges B and C, and there are also direct trunks from exchange B to exchange D and from exchange C to exchange B, the normal route for a call to exchange D would be over the trunks A-B and B-D. If the route A-B is busy an indirect or alternative route AC, C-B, B-D may be taken, for which purpose one of the ordinary trunks for calls to exchange C may be used. An alternative route between exchanges B and D may include an exchange E. 'I'he system however is not limited to the case in which there may be only one exchange in an indirect or alternative route. In each outlet to a trunk line is. connected a relay set for transmitting signals and impulses over the trunk as alternating currents oi a frequency within the speech range (voice frequency signals). The arrangements also provide, as will be clear from a consideration of what isY to follow, that the alternative route trunks` for any connection may be taken from a diierent group of second trunk selectors: from that giving access to the direct route trunks. The second trunk selector is also provided with contact positions at the end ofits bank giving access to call storing equipment associated with each trunk group and arranged to be taken into use if no direct route trunk is free at the time the wanted group is searched. Provision is made for supervisory signals to be transmitted and in the case of a call being stored, for signallingto the operater when a free trunk in the desired direct route becomes available so that the selector may be again set in motion to search for it.

The second trunk, selector is caused to search in` either a group of direct route trunks or a group of alternative route trunks in accordance with. a signal received from the register sender. If it searches a group of trunks to which there is no alternative route and congestion is encountered the callk is stored. If there is an alternative route and all the trunks in the direct route are busy, the latter are not searched but the trunks of the alternative route are searched. If at the time or" search these are all busy, the switch is brought to rest on overliow contacts different from those connected to the storing positions. The call is not stored but a signal is transmitted by a battery connection to the wire corresponding to Y in Fig. l to the register sendier to bring about release of the connection so far set up and the setting up oi a connection to the direct group of trunks. Since this group is busy the call will be stored as in the case of a trunk group to which no alternative route is provided.

The circuits shown in Figs. l-8 will now be described. These iigures should be arranged with Figs. l-4 in order and Figs. 5 8 in order below them. The register sender which is assumed to be in exchange A is one of a number connected to a chain circuit, the wires of which designated In and Out will be seen to the left of Fig. 5. The register sender is connected to a connecting circuit when required by means of a coupling switch SC. This is a latch-controlled motor-driven single motion 50-point switch with 8 wipers and associated contact arcs. Only the latch magnet is shown and this is designated SCM. The construction and method of operation or" such a motor mechanism is now well known in the art and hence for the purpose of this description only the latch magnet will be considered. The incoming signalling wires W, X, Y, Z are connected to wipers of a controlling switch which is a pawl and ratchet stepping switch of the reverse drive type. Its magnet is designated DDM and its wipers DDL-DDB. This switch serves to direct the incoming keyed up digits to the several registers in turn and afterwards to connect the registers to the signalling wiresv for the transmission of the code digits for the setting of the trunk selectors at the same exchange. The registers are of the relay type, each comprising four relays. The relays of the first register are designated AW, AX, AY, AZ, and those of successive registers CVV-CZ, DW-DZ and EW-EZ respectively. There is a further motor-driven switch for effecting translation for the received code digits. The motor mechanism of this switch isindicated by its latch magnet designated CMU and its wipers are designated CMS-CMH. The Contact arcs of wipers CMI-CMS are connected to terminals l to 8 in a manner which provides for the translation of the digits setting the switch and for Vasuitable. marking of the.l signalling io l wires. The translating switch CM is set in accordance with a marking applied by the relays of the rst two registers. The switch, in accordance with its setting also connects relays PY, SY and DG to three group control wires the condition of which is determined by the condition of the corresponding trunk groups and by a supervisory key, the throwing of which denotes that all calls are subject to delay and that delay working by the operators in force. A further pair of stepping switches of the pawl and ratchet type and designated SM and SN serve as a sender for the sending of loop impulses over wires W and X for the setting of local automatic selecting switches. Of the relays shown the principal are the high speed test relays TC and T for the switches SC and CM respectively, the release control relay B, auxiliary release control relay BA, start relay ST, start sending relay SR, change from code sending to impulsing relay SS, first trunk selector re-search relay RL, trunk group re-search relay RS and cut-oli relay CO. Relays ZA and ZB are impulse marking relays and relays PD, RP, RQ and SX are concerned with impulsing. Relay Y is an impulse generating relay which generates the impulses for stepping the switches SM and SN and in certain circumstances the switch DD, and by means of its contact yl opens and closes the wires W and X for the transmission thereover of impulses. Relay RA. is a release alarm relay connected in series with the two switch motors and relay RB is a release alarm relay having one Winding connected in series with the stepping switch magnets. The functions of the other relays not specically outlined at this point will be apparent from the following description. Contacts scon and cmon are off-normal contacts of switches SC and CM respectively, contact ddm is an armature operated contact of magnet DDM and contacts Smm and snm are similar contacts of magnets SMM and SNM. In order to simplify the drawing points indicated by like numerals enclosed in circles are assumed to be joined together.

An operator at the exchange at which the regis'ter sender of Figs. 1 8 is situated having received a demand for a trunk connection refers to her routing table to acertain the exchanges through which the call will have to pass to reach its destination. She associates her position apparatus with a free iirst trunk selector,'marks the position in the bank of the coupler switch associated with the register sender and causes a start signal to be sent over wire In to the register sender. In the register sender, relay C is normally operated in a circuit from earth over key BK, contacts b5, co3, the relay winding to battery and the In" wire is connected over contact cl to relay ST. The starting signal transmitted by the action of the operator accordingly operates relay ST. Contact stl prepares a testing circuit for switch SC, contact S752 completes a circuit for relay SH if the coupling switch SC happens to be on any contact other than zero, contact S153 completes a circuit for the coupling switch latch magnet over Contact tcl and the motor is started. Battery to the latch magnet and motor is fed over relay RA. Contact std lights the pilot lamp PL. The switch SC is rotated until the marked position is reached whereupon the high speed test relay TC operates, the circuit being from earth over contact stl, the metal rectifier, both windings of relay TC in series, wiper 8 to battery onwire P. Contact tcl opens the driving circuit and the switch is brought to rest. When the switch was started or as soon as it left its zero contact position if it starts from this position, contact scon2 was opened and relay SH operated and locked up over contacts shi and b3. If the starting signal should be removed before the marked position is met by the switch, the switch continues to rotate until the zero position is reached by reason of a circuit for the magnet SCM over contact st3, shZ and sconl, the last-mentioned contact being closed whenever the switch Wipers are away from their zero position. When the switch reaches its zero position the magnet circuit is opened at contact sconl and relay SH is shortcircuited at contact scon2 to bring about its release.

Earth over wire P operates a relay in the position circuit to connect the digit key strip to wires W-Z and to open the circuit for relay ST. The right-hand high resistance winding of relay TC and rectifier are short-circuited by contact tcl and a short-circuit is removed from the upper winding of relay B. Relay B operates in series with magnet SCM and holds to battery over contact b4. Contact bl connects a holding earth for the register relays, contact b2 disconnects winding (I) of relay CO from commoned contacts in the bank of wiper DDT, contact b3 releases relay SH and prepares a holding circuit for relay B and for a relay in the position circuit, contact b5 connects earth to magnet DDM, contact h6 releases relay C and connects earth over key BK to maintain the lamp PL glowing and contact bl connects a general holding earth over contact cia3 for many of the relays. Relay BA operates. Contact ba? closes in the circuit over wiper l and contact ba3 connects relay ZS to a time pulse circuit. Relay C releases and connects wire In to wire Out to direct the next call from any position to the next register sender in the chain circuit. Relay ST releases. 'I'he distributor takes one step, its magnet circuit being from earth over contact b5, contact O and wiper DDI, contact drlm of magnet DDM, contact rZZ, magnet DDM, low resistance winding of relay RB to battery. When the magnet armature is attracted contact ddm opens and releases the magnet and the wipers are .stepped to contacts I. There being no earth over contact I in the bank of wiper DDI the switch remains in this position. Whenever relay RA is operated, contact ral closes a circuit for the high resistance winding of relay RB and whenever relay RB is operated contact Tbl closes a circuit for a delayed alarm, contact T122 disconnects lamp PL from steady earth and connects it to a source of intermittent earth and contact T123 is included in the releasing circuit for relay CO to hold this circuit open until all the switches in the register sender have been restored to normal. In position l of the distributor, wires W-Z are connected over wipers DB2- DDS to the register relays AW-AZ.

It will rst be assumed that there is a direct trunk free and available to the next exchange on the route to the required destination and that there is no alternative route.

The operator keys up the digits indicative of the next exchange along the direct route. This designation comprises two digits. The rst digit operates one or a pair of the relays .AW-AZ. It may here be remarked that the digit l represented by a marking on wires W and X is reserved for calls to a local automatic exchange. The

relays responsive to the marking applied by the first digit key depressed operate over their lefthand windings and lock up over their right-hand windings, their contacts l and contact bl. In the operating circuits for the register relays relay DS operates over its right-hand winding. Contact dsl closes a circuit for magnet DDM, the

magnet operates and on the release of relay DS, which occurs when the digit key is released, steps the distributor to its second position in which the register relays BW-BZ are connected to wires W-Z. The second digit is registered, the relays locked up and the distributor is stepped to position 3. A third digit, the numeral l, is keyed up to cause the second trunk selector to search and register relays CW and CX are operated and locked up and the distributor steps to position Il. Contacts of the two registers set by the first two digits are connected between banks of the translating switch CM and provide a marking for the setting oi that switch. Since one of the relays AW, AX will not have been operated a circuit is closed in position 3 of the distributor from earth over contacts ck, bl, wiper DDii, contact aw@ or amil, right-hand winding of relay CS to battery. Relay CS operates and locks up over its leithand winding, contacts cs2, bl and cia3 to earth. Contact csi disconnects contact lll in the bankoi wiper DDl from commoned contacts l to 9, ll and Iii- 2d and connects it to a set of contacts of the register relays CW-, DW-, EVV- contact C33 prepares a circuit for test relays TS and TT and with contact csi opens circuits that might otherwise exist for these relays over contacts aw? and @m2, contact 035 closes a circuit for latch magnet CMU and contact est connects earth over wiper DDS when it reaches position 4 to the right-hand winding of slow operating relays AS. The latch magnet CMU operates in a circuit irom earth over contacts tl and cs in series with relay RA and the translating switch is driven in search oi the marking applied by the registers. This marking is battery over wiper CMIZ, contacts of the registers AW-AZ and BW-BZ and a conn tact in the bank of wiper CMIS. When this marking is encountered, relay T operates and at contact tl opens the circuit for CMU thereby bringing the switch to rest and closes the circuit oi relay CT. Relay CT operates and at contact ctl connects relay DG to wiper CMQ to determine whether delayed working is in force on this particular trunk group or not, at contacts cti. and ct yprepares circuits over wipers CMl and CMH to route-determining wires, at contact ctll prepares a circuit for relay PY and at conf tact ct completes the following circuit: earth, over wiper DD, contact cs, right-hand winding of relay AS, contacts dcZ, ct5 to battery. Ii delayed working is not in force relay DG will not be operated and relay AS will operate in the above traced circuit. Contact as! closes a circuit for right-hand winding o1 relay SR and contact as? connects earth over wiper 2 of switch SC to wire D to operate a relay in the position circuit to bring about the disconnection of the digit key strip and the connection of the signalling wires W-Z to the first selector code marking relays. The relay in the position circuit connects a high resistance winding to wire P over which it holds but relay TC in series with it does not receive suflicient current to maintain it and it releases. Relay SR operates. It may here be remarked that the two windings oi relay SR are wound differentially and the relay will not operate due to the energisation of both windings in series. Furthermore, relay CK which is connected in series with the right-hand winding of relay SR and in parallel with its left-hand winding will not operate in this circuit. As a result of the operation of relay SR the relay locks up over contact srl independently of contact asl and the connection tol relay CK is opened: ,contact 51'2 prepares a stepping circuit for switch DD, contact ST3 connects up the lower winding of relay B. over contacts co2 and b3, relay B holding until this connection is made by reason of its upper winding being short circuited over contact tcl. Earth over contact b3 ,and the winding of relay TC holds relay B by means of its lower winding and the relay in the position circuit connected to wire P. Contact ST4 completes the circuit of relay S and contact ST5 opens the circuit of the right-hand winding of relay DS. Relay S operates. Contact sl connects battery over relays TS and TT to those wipers or CMI-CMB connected up by the operated primary routing relay PY, contact S2 prepares a connection for relay SS, contact sicompletes the previously prepared stepping circuit for the distributor and closes a circuit for the lower winding of relay PY, contact sd opens in a path over wire Y, a parallel path being maintained closed over contact ds, and contact S5 closes in a circuit for relay CO. Magnet DDM operates in a circuit from earth over contacts s3, ST2, wiper DDI and contact ddm and the switch is stepped by self-interruption of the magnet circuit until position 'l is reached. In this position wires W--Z are connected over wipers DD2--DD5 to terminals of the cross-connecting frame crossconnected to the translating banks of the translating switch. Contact l in the bank of wiper DDB is so connected to relay RL to bring about the timing of an interval before a re-searchbyA the first trunk selector if the latter meets with congestion.

Relay PY operates, locks up over contact pyi and at that contact opens a possible operating circuit for relay SY. A further operating circuit ior relay SY is opened at contact py. Contact ps3 vdisconnects relay RS from contact 9 in the bank of wiper DDE, and contacts r11/, p11/5 and py complete the connection of relays TS and TT to wipers CMI, CH2 and CM4. The digit for setting the rst trunk selector in a direct route is marked in the banks of wipers SMI and CM2, and the digit for setting the second trunk selector in a direct route Yis marked in the banks of wipers CMS and CMt. The corresponding digits for the marking of an alternative route are marked in the banks of wipers CMS, CMG and CMl, CMS respectively. A circuit or circuits now exist irom earth over the several code marking relays in the position circuit, one or a, pair of the wires W, X, Y, Z, Wipers DB2-DB5 in position l, terminals I-il of the connecting eld, wipers CM! and/or CM2, contacts pyfi, and/or m15, cs3, dst, si, relays TT, TS, contact ttl, to battery. The code relays are operated in series with relays TT and TS. Relay TS is very quick to operate and changes over its contact tsl before contact ttl opens. When relay TT operates, contact ttl and Contact tt2 prepares a circuit for the left-hand winding of relay DS. As a consequence of the setting of the rst trunk selector in response to the applied marking, the circuit of the code marking relays is opened. Relay TS releases immediately and during the somewhat longer releasing time of relay TT a circuit for relay DS is closed. The release ci relay TT opens this circuit and releases relay DS. Relay DS by the operation and release of its contact dsl causes the distributor to take one step, contact ds2 connects relay SS to wire Z in readiness to receive a signal denoting that further digits are to be transmitted as impulses, contact ds3 connects relay RL to wire Y in readiness to receive a signal denoting a state of congestion and to initiate a pause after which a further seai'ch by the rst trunk selector will be made, and contact CISG opens a further point in the circuit for relays TT and TS to prevent their re-operation until the distributor shall have stepped. The digit for marking the second trunk selector is transmitted in a similar manner to that for the first trunk selector over wipers CM3 and CMII and their contacts cross-connected to terminals 5 to 8 of the cross-connecting eld and wipers DB2- DDE in position 8. Relay R operates in position 8 by means of its right-hand winding to release relay RM should it have been previously operated. After this marking has been transferred switch DD moves to position 9 in which a marking corresponding to the digit I is transferred to cause the second trunk selector to search in the group previously marked. The digit is transferred over relays TS and TT, contacts C102, C322 and contacts 9 in the banks of wipers DDZ and DDS. Switch DD is stepped to position I I) in which earth is extended over wiper DD'I and contact csI to Winding (I) of relay CO. Relay CO operates and locks up over contact co4. Contact co2 releases relay B and opens the circuit over wire P to the position circuit to give a signal to the operator that sending has finished. Contact co3 maintains lamp PL lit and guards against re-operation of relay C until the register sender apparatus has been completely restored to normal and contact co5 prepares for the release of relay CO.

Relay CO releases when all the apparatus in the register sender has been restored to normal and contacts 1'b3 and cmonZ are closed to shortcircuit relay CO over wiper DD'I.

Releasing circuits are closed as follows: for the distributor over contacts b5, S85, rc3 and wiper DDI to magnet DDM and relay RB; for the translating switch by the release of relay CS at b1, contact C85 closing a circuit for magnet CMU and relay RA over oir-normal contacts CmonI. Contact b1 also disconnects earth from the several relays in the register sender and contact bI unlocks the register relays. When the switches have restored, contact T173 closes and contact 01710112 being closed a short circuit is imposed across winding (I) of relay CO from earth over contacts C83, rs5, rl'l, wiper DDI in its normal position and relay CO is released opening its releasing circuit at contact co5 and re-connecting relay C at contact co3.

If the second trunk selector is not to search in a selected trunk group but is required to select a particular trunk in that group the third digit will be one of the numerals 2 0. The code marking will accordingly be transferred in the same way as for the numeral I but instead of the relays CW and CX being opearted one of these relays or a different pair will be o-perated.

If an alternative route exists, relay PY will be operated as soon as the third digit is received on the register and relay CT has operated. It should be explained that the contacts in the bank of wiper CMIO are connected to wires which are earthed by a group control device so long as there are direct routes available in the respective trunk routes. Similarly the contacts in the bank of wiper CMI I are earthed so long as alternative routes to the next exchange to be selected are available. Relay SY is slow to operate in order that preference may be given to the direct route. Accordingly when relays CW, CX and CT have operated, relay PY is operated over its upper winding and wiper CMIG and the circuit for relay SY over wiper CMI I is opened at contact 111/2. The setting of the first and second trunk selectors proceeds as described above after which the register sender is released. If all the direct trunks are busy but an alternative route is free, earth will be absent from the contact in the bank of wiper CMH) and relay SY will be operated by means 0f its lower winding. This will take place before relay S operated and contact S115 will prevent the subsequent closure of the circuit over the lower winding of relay PY when contact s3 closes. Relay SY locks up over its upper Winding and contacts sy and pfyI at contact S'Jd disconnects relay PY from Wiper CMID to guard against the transference of a mutilated code should a direct trunk now become available. Contact S112 disconnects wiper CM3 of the translating switch and connects up wiper CM1, con tact .s1/I prepares a circuit over wire Y for giving a signal to the second trunk selector that it is to search for an alternative route and that the call must not be stored if by the time this route is searched there should be no free trunk and contact S113 connects earth over wire C to give a signal to the operator to indicate to her that an alternative route is being taken. The first two digits are transferred as before in positions 'I and 8 of the controlling switch, the only diierence being that the code marking relays to be operated depend on the marking applied over wipers CMS, CMS and CM'I, CM8 instead of a marking over wipers CMI-CM4- The code marking relays for the third digit are those connected to wires W, X and Y since these wires are marked in position 9 of the distributor over contacts C102, cm2 and syl. If the alternative route is found free, the register sender is then released.

If the alternative route, although signalled free, 1s found busy by the time the second trunk selector tests the outlets of the route, the second trunk selector rotates to a predetermined contact position in which battery is connected to wire Y. The distributor will be in position 9 at this time and when as a consequence of the second trunk selectors being stopped on the predetermined contacts relay TS is released and relay DS is operated, relay RS is operated in a circuit from earth over wiper DDB, contact m13, Winding (L) of relay RS, contacts r1n3, ds, ssll and wire Y to the aforementioned battery. Contacts rsI connects earth to wire S to bring about tlie opening of the code signaling wires in the first trunk selector circuit and the release of the first and second trunk selectors, contact TS2 connects winding (II) of relay RS to the stepping circuit for magnet DDM. contact T83 connects earth to contacts 8 to IIJ in the bank of wiper DDI to cause the distributor to step to contact II and thence to contact O by reason of the extension of earth over contacts rs3 and ssi to contact positions I I-Zl. On reaching contact O the switch is stepped on due to that contact being earthed over contact b5. Contacts I-G are earthed over contacts .912 and s3, and the switch self-steps to contact 'I where it is brought to rest. Contact rs4 having closed, earth is extended to the lower winding of relay PY and that relay :is `operated to release relay SY and to cause the direct route marking to be re-applied to the first trunk selector. Contact rs holds open the circuit for relay CO during the stepping of the distributor over contact lil. Relay RS is held during the stepping of the distributor by its winding (Il) connected over contact rc2 to the seli-stepping circuit. The distributor is now in position 'l and the rst digit indicative of a trunk to the next exchange on the direct route to the call destination is transferred as before. The iirst and second trunk selectors are set in the normal manner but since there are no direct trunks availn able, the call is stored in a storage equipment particular to the trunks of the direct route and the register sender is released. If at the time relay CT operates there are neither direct nor alternative route trunks free and available and delay working has not been initiated, relay PY is operated by means of its lower Winding over contacts ctt, sy and s3 tc bring about digit trans mission for routing the call to the direct route so that it may be stored.

It will now be clear that the direct and alternative routes, which are determined before search is made by the first trunk selector may be taken from different groups of second trunk selectors. In the case oi a reversion from alternative to direct route such as has just been described, the rst trunk selector is released and re-set so that a different group of second trunk selectors from that used Vfor the alternative route may be employed.

,It may happen that the first trunk selector is unable to und a free second trunk selector to deal Awith a call although there may be free trunks in the desiredroute from the groups of second trunk selectors concerned. The code marking for the first trunk selector is applied in contact position l to the distributor. If there is no free second trunk selector available in the marked group, the selector rotates to a congesn tion position in which battery is connected to wire Y. This battery connection completes a circuit for the left-hand winding of relay RL over contact l and wiper DDt` when relay DS operates. Relay RL locks up over its right-hand winding and contacts T15 and fm2. Contact rli earths wire S to bring about release or" the iirst trunk selector from the congestion position, contact rlf opensthe self-stepping circuit for magnet DDM, contact T23 closes a circuit for relay Y, contact T24 prepares a pulsing circuit to magnet DDM., contact rlt prepares a circuit for relay RM and contacts rll opens the circuit over wiper DD'l to guard relay CO against operation when the wiper reaches contact it. Y is a pulsing relay and operates by the slow-self-interruption of its own circuit. It has two windings, in the circuit of one of which is connected a condenser QG oi a capacity suited to the pulsing speed required.

This condenser is also shunted, in the present use of relay Y by a further condenser QF over contacts S24 and TIS. When contact riti closes the condensers commence to charge and the cur= rent flowing in the windings or" the relay produce opposing uxes so that the relay does not operate immediately. As the condenser charging current dies down the ux produced by current in the right-hand winding of the relay predominates and the armature commences to move. When contact 'y2 is fully operated, the relay does not release immediately as the condenser commences to discharge through the two windings in series and the directionof the current is such that the fluxes produced act in the same direction thus delaying the release of the relay. It will thus be seen that the pulsing time and duration will depend on the value of capacity connected in series with the left-hand winding.

For the purpose now being considered, viz: the stepping of the distributor, a speed of 10 impulses per second is suitable. When contact y2 is in its front position the following circuit is closed: earth over contacts dsl, T13, oci, y2, TM, rml, magnet DDM, relay RB to battery. The magnet attracts its armature. When contact y2 opens the magnet releases its armature and advances the switch wipers one step. At each pulse given by relay Y the distributor is advanced one step and this continues until thel Wipers have been stepped round the bank until they reach contact t thus measuring off a period oi about 2.5 seconds. In this contact position a circuit is closed over wiperDD and contact rit for the left-hand winding of relay RM. Relay lRM operates and locks up over contacts'r and fm2. Contact rml opens to prevent a further pulse reaching magnet DDM and contact rm connects winding A(Il) of relay CO to contact ds in readiness to receive a congestion signal. ing circuit of relay RL and that relay releases thereby opening the circuit for relay Y. Closure of contact T12 completes a circuit over contacts s3, sr2, and wiper DDI for magnet DDM which by'takinga single stepbrings the Wipers again intothe '7th position in which the iirst coded digit'is once more transferred to the first trunk selector. If the selector is successful in nding a free outlet, the second and third coded digits are transferred to the second trunk selector but if a congested condition is still encountered, battery will be applied to wire Y and relay CO operated `to release the register sender. In position 8 of the distributor, relay R is operated to release Vrelay vRM at contact r3 to enable relay RS to receive a signal over wire Y from the second trunk selector. By arranging for the release oi relay RM on the release of relay RL an indefinite number of searches by the first trunk selector at intervals maybe had.

If traic is very heavy in the trunk group over which it is desired that the call shall proceed, delay working may be put into operation. When this is done a key is thrown which connects earth to the Yrelavant contacts in the banks of wipers CMS and CMH] of the translating switch. When the translating switch has taken up its position determined by the operation oi the relays in the first and second digit registers and relay CT has operated, relay DG operates over Contact ctl and wiper CMQ to the earth applied by the delay working key. Contact dgl connects a flicker earth to wire C to indicate to the operator that delay Working is in force on the trunk group concerned so that she may ticket the call and advise the caller accordingly. Contact dgZ opens to prevent operation of relay AS which would bring about a fruitless search by initiating the transmission of the code marking digits. Since relay PY will be operated by the earth over wiper CMlD the operator can, by pressing a key, operate relay SR directly over Wiper SC'I thereby starting digit transmission and causing the call to `be stored.

Should the operator inadvertently key up a dead number for the first two digits, the translating switch will not iind a marked contact and will continue to rotate until the last contact posi- 75.

Contact fm2 Opens the locktion is reached. It will be stopped in this position by the operation of relay T to battery over the wiper CMI2. Relay RM will operate in a circuit from earth over its right-hand winding, last Contact and wiper CMB, contact ctI, relay DG to battery, but relay DG will not be operated. Relay RM locks up over its left-hand winding, and contacts r3 and fm2 and contact T1113 prepares a connection for winding (II) of relay CO. A translation is provided for the iirst digit and this is transferred to the first trunk selector which is rotated to a predetermined position in which battery is applied to Wire Y.

When relay DS operates after the setting of the rst trunk selector the battery on wire Y operates relay CO by energising its winding (II) to release the register sender.

If the rst digits are keyed correctly but a third digit is keyed for which there is no corresponding trunk, all three digits will be transferred in the usual manner but the second trunk selector will continue to rotate to a last contact position where battery will be connected to Wire Y. Relay RS however will not operate in this instance as its circuit wil] be open at contact 21g/3 and release of the register sender will take place when the distributor is stepped to position IIJ.

On the assumption that a free trunk to a succeeding exchange along either a direct or indirect trunk route has been found the release of the register sender automatically brings about the switching through of the operators circuit to incoming apparatus at the distant end of the trunk and the operator dials the code of the next exchange to be selected in the setting up of the required trunk connection.

The operation of the register sender in setting up calls over local automatic switches will now be described. Such a call is indicated by the rst digit being I. Up to four further digits may follow for the setting of the numerical selecting switches. The rst register will record the numeral I by the operation of relays AW and AX and these relays will lock up to earth over contact bl. Contacts awt' and cm3 open and prevent the operation oi relay CS in position 3 of the controlling switch. Contacts awZ and a2 provide a marking over wires W and X to operate the code marking relays in the first trunk selector, indicative of a call to be extended to a group of' first numerical selectors. Since relay CS is not operated the translating switch does not search. As many further digits as are necessary for setting up the Connection are keyed and transmitted to one or more of the registers 13W-, CW-, DW, EW-. Furthermore, since relay CS is unoperated relay AS will not be operated in position 3 of the distributor and sending will be delayed until all the necessary numerical digits have been registered. If there are four of these, switch DD will be stepped to position 6 after the last has been recorded in which position relay AS will be operated by means of its lefthand winding. Relay AS at contact asl operates relay SR which in turn operates relay S and transmission of the registered digits commences. If there should be less than four numerical digits for the call in question, sending will be started by the operator pressing a start key. This causes a low resistance battery connection to be made to wire S which operates relay SR. The distributor is stepped to position 'I in which relays TS and TT are connected over contacts cs3, aw2 and csd, arc2, to wires W and X and the first digit is transferred to the rst trunk selector. The selector searches for a free outlet to a first numerical selector. Such an outlet contains a relay arrangement which causes battery potential to be applied to wire Z. When such an outlet is found relay TS releases and relay DS operates and the battery over wire Z is extended over contact ss3, s2, cZsZ to winding (I) of relay SS. Relay SS operates and locks up over its winding (II) and early closing contact ssl. Contact ssl, S32, ss3 and ss4 disconnect wires W-Z from wipers DB2-DDS. Contacts ssl and ss2 connect wires W and X to a loop including relay VA at present short-circuited over contacts sal and contact yi). Contact s55 applies earth over contact rs3 and contact 'I in the bank of wiper DDI to magnet DDM, to cause it to self-step the switch to position 8. A self-stepping circuit is closed over contacts 8-I0 and contact ss5 to cause the switch to drive to position II in which marking contacts in the banks of switches SM and SN are connected over Wipers DD2-DD5 to earth over the locking contacts I of operated register relays and Contact bl. Contact ss6 closes a circuit over wiper DDB in position II for relay SX which operates and locks up over contact 82:2. Contact sarl starts relay Y pulsing by applying earth over contacts S25 and oel and the circuit previously traced for this relay.

Switches SM and SN are stepping switches stepped by pulses delivered by relay Y to their magnets SMM and SNM. Associated with these switches are relays ZA and SB which operate when a pair of marked contacts are simultaneously encountered by wipers 2 and 3 of the switch in use. The switches are used alternately, the odd numbered numerical digits being marked in the banks of switch SM and the even numbered numerical digits in the bank of switch SN. Relays R, RP, RQ, SX and PD are concerned with the alternate use of the switches. Relays VA, VB and VC are concerned with the changeover from one digit to the next and relay SZ is the usual stop relay. Two speeds of impulse sending are provided for, a speed of 14 impulses per second and a speed of 10 impulses per second. The speed is controlled, as before mentioned, by the value of capacity in the circuit of the left-hand winding of relay Y and to reduce the impulsing speed for the setting of numerical selectors, which might be required in some cases where junctions are involved, a further condenser QF is switched in parallel with condenser QG normally in the relay circuit by the operation of relay SD. Whether this relay shall operate or not is determined by the second registered digit by means of a battery connection cross-connected as required to contacts of the register relays BW--BZ.

When relay SS has operated and has operated relay SX in position II of switch DD, relay Y is started by closure of Contact sx1. Contacts 8x3 and smit connect relay PD to contacts 22-24 in the banks of wipers SMI and SNI. At each pulse of relay Y, when contact 'yE closes. a circuit is closed for magnet SMM, the circuit being from earth over contacts srl, S25, vcl, y2, T14, pd3 and rl. The magnet operates and on the release of relay Y the switch magnet armature falls back and steps the switch. At each pulse of relay Y the loop over wires W and X is opened at Contact yl and an impulse is transmitted to the numerical selector connected to these Wires. If four numerical digits are to be transmitted contacts in the banks of wipers SM2 and SM3 will be marked for the counting of the first digit by earth over contact bl, locking contacts I of the operated register relays BW--BZ and wipers DB2-DDS. For the sake of example it will be assumed that the first digit is 5. Relays BX and BZ will be operated and contacts 5 in the banks of wipers SM2 and SM3 will be marked. Although contact l in the bank of wiper SMS will be marked over wire X and relay ZA will operate in this position of the switch, the stop relay SZ will not operate to stop impulse transmission. For this relay to operate relays ZA and ZB must both be operated and the markings of switches SM and SN are such that this can only occur n one position for each numeral. Switch SM is accordingly stepped until a position is reached in which both relays ZA and ZB operate. A circuit is now closed over contacts I of these relays and Contact @c3 for relay SZ. Relay SZ operates and at contact sal short-circuits contact yl to prevent the transmission of further impulses over the outgoing loop. Contact 322 completes a holding circuit for relay SZ over Contact b5 to be operative after relays ZA and SB release, contact S23 closes a further holding circuit dependent on the counting switches, contact sail disconnects condenser QF from the circuit of relay Y and connects it to a discharging circuit and the pulsing speed of relay Y is increased, contact S25 opens the pulsing circuit for relay Y and prepares a circuit including the left-hand winding of relay VC, and contact sa closes a self-stepping circuit for switch SM. Magnet SMM operates in this circuit from earth over contacts sa, T103, magnet-operated contact Smm, contacts I-ID and wiper SMI and advances the wipers rapidly to position Il. In position Il relay PD operates by the energisation of its high resistance right-hand winding in series with magnet SMM in a circuit including contacts 5x4, rpt? and wiper SMI The switch magnet does not operate in this circuit. At contact pdl the further locking circuit for relay SZ is closed, at Contact 1x12 the pulsing circuit for relay Y is reclosed and at contact m13 the right-hand winding of relay PD is shunted by the low resistance left-hand winding of the relay and magnet SMM now operates and is stepped by the now rapidly pulsing relay Y to its normal position.

If the loop over wires W and X extends metallically to the numerical selector which has just been set, the momentary break or increased inductance in the circuit caused by the operation of the switching relay thereat eiects the release of relay VA which was operated over the loop in series with the impulse receiving relay. Relay VA was short-circuited during impulse transmission and was switched into circuit on the operation of relay SZ. It is a very sensitive relay and will release under the change of loop condition above referred to. When it operates a charging circuit for condenser QH is closed over contact tal and when it releases the charged condenser is discharged over the winding of relay Relay VB is a fast relay and at its contact obI connects up a holding circuit for itself and an operating circuit for relay VC. Relay VC operates due to the energisation of its right-hand winding and contact co2 substantiates Contact tht. Contact 'UCI opens the pulsing circuits for relay Y and magnet SMM, contact U03 opens in the operating and temporary holding circuits for relay SZ and extends earth by Way of contacts b5, sa?. and T12 to magnet DDM causing it to operate and contact @c4 closes a circuit 91' the left-hand winding of relay RP. The rapid pulsing of magnet SMM ceases and contact m2 changing over on the operation of relay RP recloses the self-stepping circuit for switch SM which continues to be stepped by self-interruption to normal. Relay RP holds by means of its low resistance right-hand winding connected in the self-stepping circuit of magnet SMM by contact m3. The operation of relays VC and RP opens the circuit for relay PD and this relay releases and releases relay SZ. Contact szI falling back short-circuits relay VA and re-connects contact yl in the impulse transmitting loop and contact S25 releases relays VB and VC and recloses the pulsing circuit for relay Y. Contact sail prepares to re-ccnnect condenser QF to bring the pulsing speed again to 10 impulses per second. Contact .922 opens the circuit for magnet DDM and that magnet releases and steps the distributor to position I 2. In this position the marking for the second numerical digit is connected up and relay R is operated over wiper DDG. Contact TI disconnects the pulsing circuit for magnet SMM, and connects it to magnet SNM, and contact r2 changes over to prepare a circuit for relay RQ to be closed consequent on the second numerical selector switching through. Contact r3 is without effect at the present stage of operations. Switch SN is now stepped in a similar manner to that described for switch SM in search of a marking applied by the operated register relays of the set CW-CZ. When this marking is reached, relays ZA and ZB operate as before and impulse transmission is stopped by the operation of relay SZ. Switch SN is stepped to position II by self-interruption and after the release of relay VA and operation cf relay VC relay RQ is operated and the switch continues to self-step to its normal position. Meanwhile magnet DDM has been operated and relay PD having been operated and subsequently released the distributor is stepped to position I3. Relay R releases and the pulsing circuit is disconnected from magnet SNM and connected to magnet SMM. The third numerical digit is transmitted under the control of switch SM and after its transmission the distributor is stepped to position Ill in which relay R is again operated. The fourth numerical digit is transmitted under the control of switch SN. After its completion the distributor is ad- Vanced to position I5 in which a circuit is completed over wiper DD'I for relay CO to bring about the release of the register sender. In the connection between the trunk selectors and the local automatic switches is connected a link circuit which normally presents a metallic impulsing loop to the local switches. When relay CO operates, contact col connects wire Z to wire Y overk contact ss3 whereby battery connected to Wire Z in the link circuit as a consequence of a relay operation when the link was taken into use is applied to wire Y to bring about the connection of a feeding bridge into the circuit.

If it should happen that one of the digits is of a low value and relays RP and RQ are operated at the same time, relay SZis held over contacts pl, rql independently of relay PD until one of the relays RP and RQ is released.

If impulsing is to be carried out at 10 impulses a second, this will be determined by the first numerical digit. The first numerical digit will be transmitted at the higher speed as it has been assumed that the first numerical selectors will be in the same exchange as the trunk selector or accessible over a short junction. When the dis- 

